Phosphonium diylides afford a general synthetic method for numerous alpha,b
eta-unsaturated functions, the double bond being di- or trisubstituted. The
diamino-phosphonium diylides, obtained in the case of stabilized ones by a
new variation of die Staudinger reaction, are also interesting tools in sy
nthesis because they allow access to, for example ketenimines, phosphorus g
uanidines or triazaphosphinimines.